Let’s assume for a moment that it’s April 2019 and the UK has left the EU.

We are in the position that Brexiteers fantasise about and we have no trade agreements anywhere in the world and are trading around the world under WTO tariff regimes. Where would be the very first place we would go to in order to start discussions about a new trade agreement?

Three principles would guide our choice: gravity, comparative advantage, and the ‘dynamic’ gains from trade. Together, they suggest that, if we were developing atrade strategy from scratch, Britain would be straight on the phone to Brussels.

In the 1960s, Dutch economist Jan Tinbergen discovered that there was a close analogy between Newtonian physics and trade flows. This is intuitive –it costs less to ship goods between neighbouring countries, and the value of trade between big economies will always be higher than between small ones, simply because large economies suck in more imports.

For every percentage point increase in a country’s distance from Britain, Britain’s trade with that country fell by 0.6 per cent. And for every percentage point increase in a country’s GDP, Britain’s trade with that country grew by 2.5 per cent. If the EU buys just under half of British total exports, but its economy comprises just 18 per cent of world GDP, why does Britain trade so much with it? The answer lies in the proximity of EU member-states – on average, they are only 1,200 kilometres away from Britain.Meanwhile, the OECD members that are not in the EU – the US, Japan, Australia and so forth – are far more distant, on average, which explains why Britain exports far less to them than to the EU.

Of course, other factors explain why Britain exports less to the ‘BRICS’ emerging economies (Brazil, Russia, India, China and South Africa), despite the fact that they make up more of the world economy than the rest of the OECD. Mainly, it is because their GDP per capita is lower – poorer countries are less likely to buy Britain’s expensive, high value-added exports than richer ones.

Brexiteers want us to tear up our trade agreements and start negotiating new ones. With the end result guaranteed to be worse than what we already have, what on earth is the point?